His outfit.When Bob Kane first began writing the Batman comics, he was writing for Amalgam Comics, which was a short lived under comic book company for both DC and Marvel comics. At that time he was only called referred to as "The Bat-Man" and still referred to at times as "The Batman". The character first appeared in Detective Comics #27 (May 1939), and since then has appeared primarily in publications by DC Comics. While in Amalgam Comics, he was an Agent of S.H.I.E.L.D.